Burning velocities of R-32/O2/N2 mixtures: Experimental measurements and development of a validated detailed chemical kinetic model

Initiation and Carbene Induced Radical Chain Reactions in CH2F2 Pyrolysis

“…Such reactive blends can have lowered tropospheric lifetimes with reduced GWP's but are typically associated with increased flammability. Recent studies from the flame and kinetics groups at UTRC and NIST [6,11,12,40,41] have chosen CH 2 F 2 as a prototype HFC species to characterize flammability in refrigerants.…”

“…This is a global property of premixed mixtures of fuel and oxidizer resulting from the synergistic influence [42] of diffusivity, exothermicity, and chemical reactivity that can be used to constrain chemical kinetic models. [43] Recent studies have developed detailed kinetics models [11,12] for the decomposition and combustion of CH 2 F 2 and to predict its flammability over a range of conditions. The modeling work [12] indicates that simulations of CH 2 F 2 flame speeds were noticeably influenced by the initiation reaction (R1) with reaction of CHF + O 2 !CHFO + O being the radical propagating step with reactive O-atoms from this reaction being the subsequent source for chain branching.…”

“…Figure 11 is a simulation for CH 2 F 2 -air flames under conditions similar to those accessed in prior experimental studies. [12] The premixed freely propagating laminar flame speed code within the ANSYS CHEMKIN [35] suite of programs was used for the present flame speed simulations. The solid blue line is a simulation for an O 2 enriched (30 %), preheated (400 K), CH 2 F 2 -air flame at 3 bars using the literature model as is.…”

“…This was quite unexpected as acetylene formation was not considered in prior studies of CH 2 F 2 pyrolysis or oxidation. [8][9][10]22,23] However, the rapid formation of reactive radicals and atoms from reactions (R4) and (R5) facilitates direct reactions that form C 2 H 2 . These include the fast reaction of HCCF with H-atoms via reaction (R6) or F-atom β-scission of the CHFCH radical in reaction (R5).…”

“…In the experimental work acetylene (C 2 H 2 ) was found to be formed in similar concentrations as fluoroacetylene (HCCF). The formation of C 2 H 2 as an intermediate has not been considered in recent models [11,12] describing the pyrolysis and oxidation of CH 2 F 2 . Our calculations also reveal that H-atoms formed in reaction R4 can facilitate the rapid conversion of HCCF to C 2 H 2 via reaction R6 which are supported by the experimental observations.…”